Terminal, base station, transmission method, and reception method

ABSTRACT

A repeater generates repetition signals by repeating uplink signals over a plurality of subframes; controller sets a timing for transmitting the repetition signals, based on information indicating a transmission candidate subframe for a sounding reference signal used for measuring an uplink reception quality; and a transmitter transmits the repetition signals at the set timing.

BACKGROUND 1. Technical Field

The present disclosure relates to a terminal, a base station, atransmission method, and a reception method.

2. Description of the Related Art

In the 3rd Generation Partnership Project Long Term Evolution (3GPPLTE), Orthogonal Frequency Division Multiple Access (OFDMA) is employedas a system for downlink communication from a base station (which may becalled an eNB) to a terminal (which may be called UE (User Equipment)).Single Carrier-Frequency Division Multiple Access (SC-FDMA) is employedas a system for uplink communication from a terminal to a base station(e.g., see 3GPP TS 36.211 V12.5.0, “Evolved Universal Terrestrial RadioAccess (E-UTRA), Physical channels and modulation (Release 12),” March2015 (which may hereinafter be referred to as “Non-Patent Document 1”);3GPP TS 36.212 V12.4.0, “Evolved Universal Terrestrial Radio Access(E-UTRA), Multiplexing and channel coding (Release 12)” March 2015(which may hereinafter be referred to as “Non-Patent Document 2”); and3GPP TS 36.213 V12.5.0, “Evolved Universal Terrestrial Radio Access(E-UTRA), Physical layer procedures (Release 12),” March 2015 (which mayhereinafter be referred to as “Non-Patent Document 3”)).

In LTE, a base station performs communication by allocating resourceblocks (RBs) in a system band to a terminal in each unit of time calleda subframe. FIG. 1 illustrates a structure example of a subframe in anLTE uplink shared channel (Physical Uplink Shared Channel (PUSCH)). Asillustrated in FIG. 1, one subframe is constituted by two time slots. Ineach slot, a plurality of SC-FDMA data symbols and a demodulationreference signal (DMRS) are time-multiplexed. Upon receiving PUSCH, thebase station performs channel estimation using the DMRS. Thereafter, byusing a result of the channel estimation, the base stationdemodulates/decodes the SC-FDMA data symbols.

In an LTE uplink, in order to measure the uplink channel quality betweenthe base station and the terminal, a sounding reference signal (SRS) isused (e.g., see Non-Patent Document 1). The SRS is mapped to an SRSresource and is transmitted from the terminal to the base station. Inthis case, the base station performs cell-specific higher-layerindication to set an SRS resource candidate group including SRS resourcecandidates that are common to all terminals that are present in a cellof interest. Thereafter, the base station performs higher layerindication for each terminal to allocate SRS resources, which are asubset of the SRS resource candidate group, to each terminal to whichthe SRS resources are to be allocated. Each terminal maps an SRS to theallocated SRS resources to transmit the SRS to the base station. EachSRS resource candidate is a last SC-FDMA symbol in a subframe that is acandidate for SRS transmission (an SRS transmission candidate subframe).Also, in symbols that are SRS resource candidates, all terminals in acell for which the SRS resource candidate group is set do not performdata transmissions to thereby prevent a collision between the SRS anddata transmissions (PUSCH transmissions).

In LTE, srs-SubframeConfig and so on are defined (e.g., see Non-PatentDocument 1) as cell-specific higher-layer signaling for setting the SRSresource candidate group. FIG. 2 illustrates one example of thedefinition of srs-SubframeConfig. Srs-SubframeConfig numbers (0 to 15)in FIG. 2 are transmitted from the base station to the terminal tothereby give an instruction from the base station to the terminal withrespect to an SRS transmission period (T_(SFC)) and an offset value(Δ_(SFC)) for giving an instruction indicating a subframe in which theSRS transmission is to be started. For example, in FIG. 2, when thesrs-SubframeConfig number is 4 (Binary=0100), the transmission periodT_(SFC)=5 and the offset value Δ_(SFC)=1 are given, and thus the second(=1+Δ_(SFC)) subframe, the seventh (=1+Δ_(SFC)+(T_(SFC)×1)) subframe,the 12th (=1+Δ_(SFC)+(T_(SFC)×2)) subframe, . . . , and the(1+Δ_(SFC)+(T_(SFC)×n))th subframe are SRS transmission candidatesubframes (e.g., see FIG. 3).

Meanwhile, in recent years, machine-to-machine (M2M) communication forrealizing services through autonomous communication between applianceswithout involvement of user decision has been expected to be a schemefor supporting the future information society. A smart grid is availableas a specific application case of an M2M system. The smart grid is aninfrastructure system for efficiently providing life-supporting linesfor electricity, gas, or the like, and M2M communication is executedbetween a smart meter installed in each home or building and a centralserver to autonomously and effectively adjust a demand balance ofresources. Other application cases of the M2M communication systeminclude, for example, a monitoring system for goods management,environmental sensing, remote medical care, or the like, and remotemanagement for inventory or charging in an automatic vending machine.

In the M2M communication system, particularly, use of a cellular systemhaving a wide communication area is attracting attention. In 3GPP, informulation of LTE and LTE-Advanced standards, standardization forcellular network enhancement for M2M, called machine type communication(MTC), is conducted (e.g., RP-141660, Ericsson, Nokia Networks, “New WIproposal: Further LTE Physical Layer Enhancements for MTC,” September2014 (which may hereinafter be referred to as “Non-Patent Document 4”)),and a study is carried on specifications in which lower cost, powerconsumption reduction, and coverage enhancement (Coverage Enhancement)are requested conditions. In particular, in terminals, such as smartmeters, that hardly move, ensuring coverage is a condition in terms ofproviding services, unlike handset terminals that are often used whileusers thereof are moving. Thus, “coverage enhancement (MTC coverageenhancement)” to further increase the communication areas is a challengein order to deal with cases in which terminals (MTC terminals) thatsupport MTC are provided at unavailable places, such as basements ofbuildings, in existing LTE and LTE-Advanced communication areas.

In order to further increase the communication areas, a “repetition”technique for repeatedly transmitting the same signal a plurality oftimes is being studied in the MTC coverage enhancement. In therepetition, signals repeatedly transmitted are combined together tothereby improve reception signal power and increase the coverage (thecommunication areas).

In addition, when attention is focused on the fact that an environmentin which MTC terminals that require coverage enhancement hardly move andchannels do not vary with time is envisaged, a technology for improvingthe channel estimation accuracy can be used.

One available technology for improving the channel estimation accuracyis “cross-subframe channel estimation and symbol level combining” (e.g.,see R1-150312, Panasonic, “Discussion and performance evaluation onPUSCH coverage enhancement” (which may hereinafter be referred to as“Non-Patent Document 5”)). In the cross-subframe channel estimation andthe symbol level combining, the base station performs, for each symbol,coherent combining on signals, repeatedly transmitted over a pluralityof subframes (N_(Rep) subframes), over a number of subframes (Xsubframes) which is the same as or smaller than the number ofrepetitions, as illustrated in FIG. 4. Thereafter, the base station usesa DMRS resulting from the coherent combining to perform channelestimation and uses an obtained channel estimation result todemodulate/decode SC-FDMA data symbols.

When the number (X) of subframes which is a unit with which thecross-subframe channel estimation and the symbol level combining areperformed is smaller than the number of repetitions (N_(Rep)), the basestation combines (N_(Rep)/X) symbols resulting from thedemodulation/decoding.

It has become apparent that use of the cross-subframe channel estimationand the symbol level combining makes it possible to improve the PUSCHtransmission quality, compared with simple repetition in which channelestimation and SC-FDMA data symbol demodulation/decoding are performedfor each subframe (e.g., see R1-150312, Panasonic, “Discussion andperformance evaluation on PUSCH coverage enhancement” (which mayhereinafter be referred to as “Non-Patent Document 5”)).

In cells that support MTC terminals, it is necessary to make the MTCterminals and existing LTE terminals coexist, and it is desirable tosupport the MTC terminals so as to minimize influences on the existingLTE systems. Thus, for example, in uplink transmission (e.g., PUSCHtransmission) of an MTC terminal (an MTC coverage enhancement terminal)which requires repetition transmission, no data transmission isperformed with SRS resource candidates, as described above, in order toprevent a collision with an SRS of an existing LTE system. This makes itpossible to prevent a collision between an SRS and data transmissions ofthe MTC coverage enhancement terminal.

Meanwhile, the above-described technology for improving the channelestimation accuracy assumes that reception signals over a plurality ofsubframes (X subframes) can be subjected to coherent combining, and isbased on the premise that transmission-signal phase discontinuity doesnot occur in at least X subframes in the repetition transmission. In therepetition transmission, there is also the consideration that thetransmission-signal phase discontinuity does not occur, unless thetransmit power and the central frequency of radio frequencies (RFs)change (e.g., see R1-152528, RAN4, “LS Out on Additional Aspects forMTC,” May 2015 (which may hereinafter be referred to as “Non-PatentDocument 6”)).

However, when any of subframes in which the repetition transmission isperformed is an SRS transmission candidate subframe, no data istransmitted in a last SC-FDMA symbol in the SRS transmission candidatesubframe. In this case, since the transmit power for the last SC-FDMAsymbol in the SRS transmission candidate subframe becomes 0, a change inthe transmit power occurs in a repetition transmission duration. Thus,the condition on which the above-described transmission-signal phasediscontinuity does not occur is not satisfied, and thus there is apossibility that phase discontinuity occurs in repetition signals. Whenthe transmission-signal phase discontinuity occurs as described above,the base station becomes unable to perform coherent combining onreception signals over X subframes and thus cannot sufficiently obtainthe effect of improving the channel estimation accuracy.

One non-limiting and exemplary embodiment provides a base station, aterminal, a transmission method, and a reception method that can improvethe channel estimation accuracy by performing cross-subframe channelestimation and symbol level combining.

SUMMARY

In one general aspect, the techniques disclosed here feature a terminalincluding: a repeater (repetition unit) that generates repetitionsignals by repeating uplink signals over a plurality of subframes; acontroller (control unit) that sets a timing for transmitting therepetition signals, based on information indicating a transmissioncandidate subframe for an SRS used for measuring an uplink channelquality; and a transmitter (transmitting unit) that transmits therepetition signals at the set timing.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

According to one aspect of the present disclosure, it is possible toimprove the channel estimation accuracy by performing cross-subframechannel estimation and symbol level combining.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating one example of a subframe structure ofPUSCH;

FIG. 2 is a table illustrating one example of the definition ofsrs-SubframeConfig;

FIG. 3 is a diagram illustrating SRS transmission candidate subframesand a setting example of SRS resources;

FIG. 4 is an operation example of cross-subframe channel estimation andsymbol level combining;

FIG. 5 is a diagram illustrating an arrangement example of MTCnarrowbands;

FIG. 6 is a block diagram illustrating the configuration of a majorportion of a base station according to a first embodiment;

FIG. 7 is a block diagram illustrating the configuration of a majorportion of a terminal according to the first embodiment;

FIG. 8 is a block diagram illustrating the configuration of the basestation according to the first embodiment;

FIG. 9 is a block diagram illustrating the configuration of the terminalaccording to the first embodiment;

FIG. 10 is a diagram illustrating an arrangement example of MTCnarrowbands according to the first embodiment;

FIG. 11 is a diagram illustrating an arrangement example of MTCnarrowbands;

FIG. 12 is a diagram illustrating an arrangement example of MTCnarrowbands according to a second embodiment;

FIG. 13 is a diagram illustrating an arrangement example of MTCnarrowbands according to a third embodiment;

FIG. 14 is a diagram illustrating an arrangement example of MTCnarrowbands according to the third embodiment; and

FIG. 15 is a diagram illustrating an arrangement example of MTCnarrowbands according to a fourth embodiment.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described below in detailwith reference to the accompanying drawings.

[Overview of Communication System]

A communication system according to each embodiment of the presentdisclosure includes a base station 100 and a terminal 200 that support,for example, an LTE-Advanced system.

Also, assume a case in which the terminal 200 (an MTC coverageenhancement terminal) to which an MTC coverage enhancement mode isapplied is present in a cell of the base station 100. For example, whenthe MTC coverage enhancement mode is applied, the above-describedtechnology for improving the channel estimation accuracy is applied tothe terminal 200.

Also, in MTC for which a study on specifications is promoted byLTE-Advanced Release 13, MTC terminals support only a 1.4 MHz frequencybandwidth (which may be referred to as an “MTC narrowband”) in order toachieve lower cost of terminals. Also, frequency hopping has beenintroduced in which the 1.4 MHz frequency band to which transmissionsignals of an MTC terminal are allocated are hopped every certainsubframes in a system band (e.g., see R1-151454, MCC Support, “FinalReport of 3GPP TSG RAN W G1 #80 v1.0.0,” February 2015 (which mayhereinafter be referred to as “Non-Patent Document 7”)).

When the frequency hopping is applied, the above-described technologyfor improving the channel estimation accuracy also needs to be appliedat the same time, and thus, an MTC terminal needs to transmit signals inX subframes by using the same resource. It is also conceivable toreserve one subframe (1 ms) or so as a time (retuning time) required forswitching carrier frequencies during frequency hopping.

In particular, in uplink transmission of an MTC coverage enhancementterminal which involves a large number of repetitions, it is assumedthat the MTC coverage enhancement terminal changes an MTC narrowband (a1.4 MHz frequency band) (frequency hopping) after transmittingrepetition signals in X consecutive subframes by using the same resourceand transmits the repetition signals in X consecutive subframes by usingthe same resource after the change, as illustrated in FIG. 5.

The value (the number of subframes) obtained by adding a parameter X (inFIG. 5, four subframes), which indicates the number of consecutivesubframes in which the repetition signals are transmitted, and aretuning time (in FIG. 5, one subframe) may hereinafter be referred toas a parameter Y (in FIG. 5, five subframes) indicating a frequencyhopping cycle. The retuning time is not limited to one subframe.

Also, the communication system includes a terminal (not illustrated)that supports an existing LTE system. As described above, in LTE, it isassumed that srs-SubframeConfig and so on illustrated in FIG. 2 aredefined as one example of cell-specific higher-layer signaling forsetting an SRS resource candidate group.

In this case, in order for the base station 100 to performcross-subframe channel estimation and symbol level combining, the Xsubframes need to be consecutive subframes that are not set in an SRStransmission candidate subframe. That is, the value of X needs to be setto be the same as or smaller than the number of consecutive subframesthat are not set in an SRS transmission candidate subframe. The numberof consecutive subframes that are not set in an SRS transmissioncandidate subframe is, for example, four subframes forsrs-SubframeConfig=3 (for T_(SFC)=5 and Δ_(SFC)={0}) and is, forexample, three subframes for srs-SubframeConfig=7 (for T_(SFC)=5 andΔ_(SFC)={0, 1}). The same also applies to other srs-SubframeConfig. Forexample, it can be said that cross-subframe channel estimation andsymbol level combining over X=4 subframes work in the case ofsrs-SubframeConfig=3, 4, 5, 6, 9, 10, 11, 12 in which the number ofconsecutive subframes that are not set in an SRS transmission candidatesubframe is four or more.

Accordingly, in each embodiment of the present disclosure, the basestation 100 and the terminal 200 set the positions of X subframes inwhich the cross-subframe channel estimation and the symbol levelcombining are to be performed, on the basis of srs-SubframeConfigindicating SRS transmission candidate subframes. This minimizes aninfluence of a collision between an uplink transmission of an MTCcoverage enhancement terminal which requires repetition transmission andan SRS of an existing LTE system, and by using a sufficient number ofsubframes, the base station 100 can perform cross-subframe channelestimation and symbol level combining, so as to improve the channelestimation accuracy.

The following description will be given of a method for avoiding acollision between a repetition transmission of an MTC coverageenhancement terminal and an SRS of an existing system and for improvingthe channel estimation accuracy by performing cross-subframe channelestimation and symbol level combining.

FIG. 6 is a block diagram illustrating the configuration of a majorportion of the base station 100 according to each embodiment of thepresent disclosure. In the base station 100 illustrated in FIG. 6, onthe basis of information (e.g., srs-SubframeConfig) indicating atransmission candidate subframe for a sounding reference signal (SRS)used for measuring an uplink channel quality, a control unit 101 sets atiming at which the terminal 200 transmits the repetition signalsgenerated by repeating an uplink signal over a plurality of subframes. Areceiving unit 110 receives the repetition signals, and a combining unit113 performs coherent combining on the repetition signals in theplurality of subframes, on the basis of the set timing.

Also, FIG. 7 is a block diagram illustrating the configuration of amajor portion of the terminal 200 according to each embodiment of thepresent disclosure. In the terminal 200 illustrated in FIG. 7, arepetition unit 212 repeats an uplink signal over a plurality ofsubframes to generate repetition signals. A control unit 206 sets atiming for transmitting the repetition signals on the basis ofinformation (e.g., srs-SubframeConfig) indicating a transmissioncandidate subframe for an SRS used for measuring an uplink channelquality, and a transmitting unit 216 transmits the repetition signals atthe set timing.

First Embodiment [Configuration of Base Station]

FIG. 8 is a block diagram illustrating the configuration of the basestation 100 according to a first embodiment of the present disclosure.In FIG. 8, the base station 100 has the control unit 101, a controlsignal generating unit 102, an encoding unit 103, a modulating unit 104,a signal allocating unit 105, an Inverse Fast Fourier Transform (IFFT)unit 106, a cyclic prefix (CP) attaching unit 107, a transmitting unit108, an antenna 109, the receiving unit 110, a CP removing unit 111, aFast Fourier Transform (FFT) unit 112, the combining unit 113, ademapping unit 114, a channel estimating unit 115, an equalizing unit116, a demodulating unit 117, a decoding unit 118, and a determiningunit 119.

Considering the amount of SRS resources needed for each of a pluralityof existing LTE terminals that are present in a cell covered by the basestation 100, the control unit 101 determines an SRS resource candidategroup in the cell and outputs information indicating the determined SRSresource candidate group to the control signal generating unit 102. TheSRS resource candidate group is selected, for example, from the tableillustrated in FIG. 2.

The control unit 101 identifies, in the SRS resource candidate group,subframes in which the terminal 200 performs PUSCH repetitiontransmission and outputs information indicating the identified subframesto the combining unit 113.

Also, the control unit 101 determines allocation of PUSCH for an MTCcoverage enhancement terminal. In this case, the control unit 101determines frequency allocation resources, a modulating/encoding method,and so on indicated by an instruction to be given to the MTC coverageenhancement terminal and outputs information regarding the determinedparameters to the control signal generating unit 102.

The control unit 101 also determines an encoding level for controlsignals and outputs the determined encoding level to the encoding unit103. The control unit 101 also determines resources (downlink resources)to which the control signals are to be mapped and outputs informationregarding the determined resources to the signal allocating unit 105.

The control unit 101 also determines a coverage enhancement level forthe MTC coverage enhancement terminal and outputs, to the control signalgenerating unit 102, information regarding the determined coverageenhancement level or the number of repetitions needed for PUSCHtransmission at the determined coverage enhancement level. Also, basedon the information regarding the coverage enhancement level or thenumber of repetitions needed for PUSCH transmission, the control unit101 generates information regarding the value of the parameter X orparameter Y that the MTC coverage enhancement terminal uses for thePUSCH repetition. The control unit 101 outputs the generated informationto the control signal generating unit 102.

The control unit 101 may independently determine the value of Xregardless of the information about the SRS resource candidate group ormay determine the value of X so that cross-subframe channel estimationand symbol level combining work by using the information about the SRSresource candidate group.

The control signal generating unit 102 generates control signals for theMTC coverage enhancement terminal. The control signals include a signalfor a cell-specific higher layer, a signal for a UE-specific higherlayer, or an uplink grant (UL grant) that gives an instruction for PUSCHallocation.

The uplink grant is constituted by a plurality of bits and includesinformation that gives an instruction indicating frequency allocationresources, a modulating/encoding system, and so on. The uplink grant mayalso include information regarding the coverage enhancement level or thenumber of repetitions needed for PUSCH transmission and informationregarding the value of the parameter X or Y used for PUSCH repetition.

The control signal generating unit 102 generates a control-informationbit sequence by using control information input from the control unit101 and outputs the generated control-information bit sequence (controlsignals) to the encoding unit 103. Since the control information may betransmitted to a plurality of terminals 200, the control signalgenerating unit 102 generates the bit sequence by including a terminalID of each terminal 200 in the control information for each terminal200. For example, a cyclic redundancy check (CRC) bit masked by theterminal ID of a destination terminal is attached to the controlinformation.

Also, the information about the SRS resource candidate group isindicated to the MTC coverage enhancement terminal (more specifically,the control unit 206 described below) by using cell-specific higherlayer signals. The information regarding the coverage enhancement levelor the number of repetitions needed for PUSCH transmission may beindicated to the MTC coverage enhancement terminal via signaling of aUE-specific higher layer or may be indicated using an uplink grant thatgives an instruction for PUSCH allocation, as described above. Also, theinformation regarding the values of the parameters X and Y used forPUSCH repetition may be similarly indicated to the MTC coverageenhancement terminal via signaling of a UE-specific higher layer or maybe indicated using an uplink grant that gives an instruction for PUSCHallocation. In addition, when the information regarding the values ofthe parameters X and Y used for PUSCH repetition is a parameterpredefined in a standard, the information does not necessarily have tobe indicated from the base station 100 to the terminal.

In accordance with the encoding level indicated by the instruction fromthe control unit 101, the encoding unit 103 encodes the control signals(the control-information bit string) received from the control signalgenerating unit 102 and outputs the encoded control signals to themodulating unit 104.

The modulating unit 104 modulates the control signals received from theencoding unit 103 and outputs the modulated control signals (a symbolsequence) to the signal allocating unit 105.

The signal allocating unit 105 maps the control signals (the symbolsequence), received from the modulating unit 104, to a resourceindicated by the instruction from the control unit 101. A controlchannel to which the control signals are to be mapped may be a physicaldownlink control channel (PDCCH) for MTC or may be an enhanced PDCCH(EPDCCH). The signal allocating unit 105 outputs, to the IFFT unit 106,signals of a downlink subframe including PDCCH for MTC or EPDCCH towhich the control signals are mapped.

The IFFT unit 106 performs IFFT processing on the signals received fromthe signal allocating unit 105 to thereby convert the frequency-domainsignals into time-domain signals. The IFFT unit 106 outputs thetime-domain signals to the CP attaching unit 107.

The CP attaching unit 107 attaches a CP to the signals received from theIFFT unit 106 and outputs, to the transmitting unit 108, signals (OFDMsignals) to which the CP is attached.

The transmitting unit 108 performs radio-frequency (RF) processing, suchas digital-to-analog (D/A) conversion or up-conversion, on the OFDMsignals received from the CP attaching unit 107 and transmits resultingradio signals to the terminal 200 via the antenna 109.

The receiving unit 110 performs RF processing, such as down-conversionor analog-to-digital (A/D) conversion, on uplink signals (PUSCH) fromthe terminal 200, the uplink signals being received via the antenna 109,and outputs resulting reception signals to the CP removing unit 111. Theuplink signals (PUSCH) transmitted from the terminal 200 include signalson which repetition processing over a plurality of subframes isperformed.

The CP removing unit 111 removes the CP attached to the receptionsignals received from the receiving unit 110 and outputs, to the FFTunit 112, the signals from which the CP is removed.

The FFT unit 112 performs FFT processing on the signals received fromthe CP removing unit 111 to decompose the signals into signal strings ina frequency domain, extracts signals corresponding to PUSCH subframes,and outputs the extracted signals to the combining unit 113.

By using information regarding subframes in which the MTC coverageenhancement terminal performs PUSCH repetition transmission, theinformation being input from the control unit 101, the combining unit113 performs coherent combining on, with respect to a PUSCH over aplurality of subframes in which the repetition transmission isperformed, data signals and signals of portions corresponding to a DMRSthrough use of symbol level combining. The combining unit 113 outputsthe combined signals to the demapping unit 114.

The demapping unit 114 extracts a PUSCH subframe portion allocated tothe terminal 200 from the signals received from the combining unit 113.The demapping unit 114 also decomposes the extracted PUSCH subframeportion for the terminal 200 into DMRS and data symbols (SC-FDMA datasymbols), outputs the DMRS to the channel estimating unit 115, andoutputs the data symbols to the equalizing unit 116.

The channel estimating unit 115 performs channel estimation using theDMRS input from the demapping unit 114. The channel estimating unit 115outputs obtained channel estimation values to the equalizing unit 116.

By using the channel estimation values input from the channel estimatingunit 115, the equalizing unit 116 equalizes the data symbols input fromthe demapping unit 114. The equalizing unit 116 outputs the equalizeddata symbols to the demodulating unit 117.

The demodulating unit 117 applies inverse discrete Fourier transform(IDFT) processing to the SC-FDMA data symbols in the frequency domain,the data symbols being input from the equalizing unit 116, to convertthe data symbols into time-domain signals and then performs datademodulation. Specifically, the demodulating unit 117 converts thesymbol sequence into a bit string on the basis of a modulation systemindicated by the instruction given to the terminal 200 and outputs theobtained bit string to the decoding unit 118.

The decoding unit 118 performs error correction decoding on the bitstring input from the demodulating unit 117 and outputs the decoded bitstring to the determining unit 119.

The determining unit 119 performs error detection on the bit stringinput from the decoding unit 118. The error detection is performed usinga CRC bit attached to the bit string. When a determination result of theCRC bit indicates that there is no error, the determining unit 119extracts the received data and outputs an acknowledgement (ACK). On theother hand, when the determination result of the CRC bit indicates thatthere is error, the determining unit 119 outputs a negativeacknowledgement (NACK). The ACK and NACK output by the determining unit119 are used for re-transmission control processing in a processingunit, which is not illustrated.

[Configuration of Terminal]

FIG. 9 is a block diagram illustrating the configuration of the terminal200 according to the first embodiment of the present disclosure. In FIG.9, the terminal 200 has an antenna 201, a receiving unit 202, a CPremoving unit 203, an FFT unit 204, an extracting unit 205, the controlunit 206, a DMRS generating unit 207, an encoding unit 208, a modulatingunit 209, a multiplying unit 210, a DFT unit 211, the repetition unit212, a signal allocating unit 213, an IFFT unit 214, a CP attaching unit215, and the transmitting unit 216.

The receiving unit 202 performs RF processing, such as down-conversionor AD conversion, on the radio signals (PDCCH for MTC or EPDCCH)received from the base station 100 via the antenna 201 to obtainbaseband OFDM signals. The receiving unit 202 outputs the OFDM signalsto the CP removing unit 203.

The CP removing unit 203 removes the CP attached to the OFDM signalsreceived from the receiving unit 202 and outputs, to the FFT unit 204,signals from which the CP is removed.

By performing FFT processing on the signals received from the CPremoving unit 203, the FFT unit 204 converts the time-domain signalsinto frequency-domain signals. The FFT unit 204 outputs thefrequency-domain signals to the extracting unit 205.

The extracting unit 205 performs blind decoding on the frequency-domainsignals (PDCCH for MTC or EPDCCH) received from the FFT unit 204 andattempts to decode control signals sent to the terminal 200. A CRCmasked by the terminal ID of the terminal is attached to the controlsignals sent to the terminal 200. Thus, when CRC determination issuccessful as a result of the blind decoding, the extracting unit 205extracts the control information and outputs the control information tothe control unit 206.

The control unit 206 controls PUSCH transmission on the basis of thecontrol signals input from the extracting unit 205. Specifically, on thebasis of the PUSCH resource allocation information included in thecontrol signals, the control unit 206 gives, to the signal allocatingunit 213, an instruction for resource allocation during PUSCHtransmission. Also, on the basis of encoding/modulating systeminformation included in the control signals, the control unit 206 gives,to the encoding unit 208, an instruction indicating an encoding systemduring PUSCH transmission and gives, to the modulating unit 209, aninstruction indicating a modulation system during PUSCH transmission.

Also, when the control signals include the information regarding thecoverage enhancement level or the information regarding the number ofrepetitions needed for the PUSCH transmission, the control unit 206determines the number of repetitions during PUSCH repetitiontransmission, on the basis of the included information. The control unit206 gives, to the repetition unit 212, an instruction for theinformation indicating the determined number of repetitions. Also, whenthe control signal includes information regarding the value of theparameter X or Y used for PUSCH repetition, the control unit 206 gives,to the signal allocating unit 213, an instruction for the resourceallocation during PUSCH repetition transmission, on the basis of theincluded information.

Also, when the information regarding the coverage enhancement level orthe information regarding the number of repetitions needed for the PUSCHtransmission is indicated from the base station 100 by using a higherlayer, the control unit 206 determines the number of repetitions duringPUSCH repetition transmission, on the basis of the indicatedinformation. The control unit 206 gives an instruction indicating thedetermined information to the repetition unit 212. Similarly, when theinformation regarding the value of the parameter X or Y used for PUSCHrepetition is indicated from the base station 100 by using a higherlayer, the control unit 206 gives, to the signal allocating unit 213, aninstruction for resource allocation during PUSCH repetitiontransmission, on the basis of the indicated information.

Also, the control unit 206 identifies, in the SRS resource candidategroup indicated from the base station 100 by using a cell-specifichigher layer, subframes in which PUSCH repetition transmission isperformed, and outputs the identified subframes to the signal allocatingunit 213.

The DMRS generating unit 207 generates a DMRS and outputs the generatedDMRS to the multiplying unit 210.

The encoding unit 208 attaches a CRC bit, masked by the terminal ID ofthe terminal 200, to input transmission data (uplink data), performserror-correction encoding, and outputs an encoded bit string to themodulating unit 209.

The modulating unit 209 modulates the bit string received from theencoding unit 208 and outputs modulated signals (a data symbol sequence)to the multiplying unit 210.

The multiplying unit 210 performs time multiplexing on the data symbolsequence input from the modulating unit 209 and the DMRS input from theDMRS generating unit 207 and outputs multiplexed signals to the DFT unit211.

The DFT unit 211 applies a DFT to the signals input from the multiplyingunit 210 to generate frequency-domain signals and outputs the generatedfrequency-domain signals to the repetition unit 212.

When the local terminal is in an MTC coverage enhancement mode, therepetition unit 212 repeats the signals input from the DFT unit 211 overa plurality of subframes to generate repetition signals, on the basis ofthe number of repetitions indicated by the instruction from the controlunit 206. The repetition unit 212 outputs the repetition signals to thesignal allocating unit 213.

The signal allocating unit 213 maps the signals, received from therepetition unit 212, to PUSCH time/frequency resources indicated by theinstruction from the control unit 206. The signal allocating unit 213outputs, to the IFFT unit 214, the PUSCH signals to which the signalsare mapped.

The IFFT unit 214 generates time-domain signals by performing IFFTprocessing on the frequency-domain PUSCH signals input from the signalallocating unit 213. The IFFT unit 214 outputs the generated signals tothe CP attaching unit 215.

The CP attaching unit 215 attaches a CP to the time-domain signalsreceived from the IFFT unit 214 and outputs, to the transmitting unit216, the signals to which the CP is attached.

The transmitting unit 216 performs RF processing, such as D/A conversionor up-conversion, on the signals received from the CP attaching unit 215and transmits radio signals to the base station 100 via the antenna 201.

[Operations of Base Station 100 and Terminal 200]

A detailed description will be given of operations of the base station100 and the terminal 200 having the above-described configurations.

The following description will be given of a case in which the SRStransmission period (T_(SFC)) is 5 or 10 and only one SRS transmissioncandidate subframe exists in the SRS transmission period (T_(SFC))(i.e., a case in which Δ_(SFC) has only one value). That is, thedescription will be given of a case of srs-SubframeConfig=3, 4, 5, 6, 9,10, 11, 12 illustrated in FIG. 2.

The base station 100 indicates srs-SubframeConfig to the terminal 200 incell-specific higher layer signaling for setting an SRS resourcecandidate group.

Also, the base station 100 indicates the number of repetitions (N_(Rep))to the terminal 200 before PUSCH transmission/reception. The number ofrepetitions (N_(Rep)) may be indicated from the base station 100 to theterminal 200 via a UE-specific higher layer or may be indicated usingPDCCH for MTC.

The base station 100 may also indicate the value of the parameter X tothe terminal 200 before PUSCH transmission/reception.

The terminal 200 performs repetition transmission on a PUSCH a number oftimes corresponding to the number of repetitions (N_(Rep)) indicatedfrom the base station 100. When the number of repetitions (N_(Rep)) islarger than X, the terminal 200 transmits the repetition signals in Xconsecutive subframes by using the same resource, then changes the 1.4MHz frequency band (an MTC narrowband) through frequency hopping, andagain transmits the repetition signals in X consecutive subframes byusing the same resource, as illustrated in FIG. 5. That is, with respectto the repetition signals, frequency hopping is performed every Xconsecutive subframes of N_(Rep) subframes. As illustrated in FIG. 5, aretuning time (e.g., corresponding to one subframe) is reserved duringthe frequency hopping.

In this case, the terminal 200 sets a timing for transmitting therepetition signals on the basis of srs-SubframeConfig (informationindicating SRS transmission candidate subframes) indicated from the basestation 100. Specifically, in PUSCH repetition transmission, theterminal 200 maps the repetition signals (an MTC narrowband),transmitted in X consecutive subframes, so as not to overlap the SRStransmission candidate subframes indicated by srs-SubframeConfig.

FIG. 10 illustrates a mapping example of signals in MTC narrowbands forsrs-SubframeConfig=3 and X=4. Also, in FIG. 10, it is assumed that thenumber of repetitions N_(Rep)=12.

For srs-SubframeConfig=3, the SRS transmission period (T_(SFC))=5 andΔ_(SFC)=0 are given (see FIG. 2). Thus, in FIG. 10, a first subframe, asixth subframe, an 11th subframe, and a 16th subframe are SRStransmission candidate subframes. That is, in FIG. 10, the number ofconsecutive subframes that are not set in the SRS transmission candidatesubframes is five subframes.

In FIG. 10, the terminal 200 transmits the repetition signals in thesecond to fifth four consecutive subframes, the seventh to tenth fourconsecutive subframes, and the 12th to 15th four consecutive subframes.That is, the individual X=4 subframes to which the repetition signalsare mapped are consecutive subframes that are not set in the SRStransmission candidate subframes. Thus, the repetition signals (the MTCnarrowband) continuously transmitted in X subframes are mapped to thesubframes so as not to overlap the SRS transmission candidate subframesindicated by srs-SubframeConfig.

In this case, in FIG. 10, the value of X (X=4) is smaller than the SRStransmission period (T_(SFC))=5. That is, the value of X (X=4) issmaller than or equal to the number of consecutive subframes (4subframes) that are not set in the SRS transmission candidate subframes.The same also applies to a case of srs-SubframeConfig=4, 5, 6 in whichthe transmission period (T_(SFC)) and the number of Δ_(SFC) are the sameas those in the case of srs-SubframeConfig=3. That is, in the case ofsrs-SubframeConfig=3, 4, 5, 6, it is possible to perform cross-subframechannel estimation and symbol level combining over X=2, 3, 4 subframes.Similarly, in the case of srs-SubframeConfig=9, 10, 11, 12, the numberof consecutive subframes that are not set in the SRS transmissioncandidate subframes is nine subframes, thus making it possible toperform cross-subframe channel estimation and symbol level combiningover X=2, 3, 4, 5, 6, 7, 8, 9 subframes.

That is, any of values that are smaller than or equal to the number ofconsecutive subframes that are not set in the SRS transmission candidatesubframes is set for the parameter X, which is a unit of processing forthe cross-subframe channel estimation and the symbol level combining. Asdescribed above, when the value of X is smaller than or equal to thenumber of consecutive subframes that are not set in the SRS transmissioncandidate subframes (or is smaller than the transmission periodT_(SFC)), the terminal 200 can map the repetition signals to subframesother than the SRS transmission candidate subframes. Thus, the terminal200 can map the repetition signals transmitted in X consecutivesubframes in which the cross-subframe channel estimation and the symbollevel combining are to be performed, while avoiding the SRS transmissioncandidate subframes.

Also, in the example in FIG. 10, the first subframes of the X=4subframes (the MTC narrowbands) in which the repetition signals arecontinuously transmitted are set in the second subframe, the seventhsubframe, and the 12th subframe, which are the next subframes of the SRStransmission candidate subframes. With this setting, the terminal 200can map the repetition signals by making best use of the consecutivesubframes that are not set in SRS transmission candidate subframes.

In particular, when the value of X is smaller than or equal to thenumber of consecutive subframes that are not set in the SRS transmissioncandidate subframes, the terminal 200 can map the repetition signals,while reliably avoiding SRS transmission candidate subframes by settingthe first subframes of X subframes in the next subframes of thecorresponding SRS transmission candidate subframes.

Similarly to the terminal 200, the base station 100 also sets(identifies) a timing of subframes in which the repetition signals inPUSCH repetition are transmitted from the terminal 200, on the basis ofsrs-SubframeConfig set for the terminal 200. The base station 100 thenperforms coherent combining on the repetition signals transmitted over aplurality of subframes, on the basis of the set subframe timing.

As described above, in the present embodiment, the base station 100 andthe terminal 200 set the timing for transmitting the PUSCH repetitionsignals, on the basis of the SRS transmission candidate subframesindicated by srs-SubframeConfig. In accordance with the SRS transmissioncandidate subframes, the base station 100 and the terminal 200 adjustthe transmission timing of the repetition signals to be transmitted inconsecutive X subframes, thereby making it possible to avoid a collisionbetween a repetition transmission of an MTC coverage enhancementterminal and an SRS of an existing LTE system.

In addition, since a value smaller than or equal to the number ofconsecutive subframes that are not set in the SRS transmission candidatesubframes is set for the parameter X for continuous transmission of therepetition signals, the X subframes include no SRS transmissioncandidate subframe, and thus phase discontinuity does not occur in therepetition transmission signals.

Thus, according to the present embodiment, in the base station 100,cross-subframe channel estimation and symbol level combining using Xsubframes are performed to thereby make it possible to improve thechannel estimation accuracy and the reception quality.

In FIG. 10, the description has been given of a case in which the firstsubframes for the repetition signals (the MTC narrowbands) in PUSCHrepetition are set in the next subframes of the SRS transmissioncandidate subframes. However, the repetition signals (the MTCnarrowbands) are not limited to a case in which they include the nextsubframes of the SRS transmission candidate subframes, and therepetition signals may be mapped to any of consecutive subframes inwhich the SRS transmission candidate subframes are not set. That is, itis sufficient that the X subframes be mapped to consecutive subframesthat are not set in SRS transmission candidate subframes. For example,the last subframes for the repetition signals (the MTC narrowbands) maybe set in the respective subframes one before the SRS transmissioncandidate subframes.

Second Embodiment

As described above, the parameter Y is a frequency hopping cycleobtained by adding the retuning time (in this case, one subframe) to Xconsecutive subframes (X≤Y).

FIG. 11 illustrates a mapping example of signals in MTC narrowbands inthe case of srs-SubframeConfig=9, X=4,and Retuning time=1 subframe(i.e., Y=5).

Also, in FIG. 11, the repetition signals are mapped so that the firstsubframes of X=4 subframes in which the repetition signals arecontinuously transmitted are the next subframes of SRS transmissioncandidate subframes. That is, in FIG. 11, the second and 12th subframes,which are the next subframes of the SRS transmission candidatesubframes, are the first subframes of X=4 subframes.

In this case, for srs-SubframeConfig=9, the SRS transmission period(T_(SFC))=10 and Δ_(SFC)=0 are given, and thus the transmission periodT_(SFC) has twice the length of Y. Also, for srs-SubframeConfig=9, thenumber of consecutive subframes that are not set in the SRS transmissioncandidate subframes is nine subframes. That is, in FIG. 11, of the 9consecutive subframes that are not set in the SRS transmission candidatesubframes, the subframes other than the four subframes in which therepetition signals (the MTC narrowband) are mapped and one subframe setfor the retuning time are four subframes. The number of remainingsubframes is equal to the parameter X.

As described above, for T_(SFC)≥Y (n is an integer greater than or equalto 2), when the first subframes of X subframes in which the repetitionsignals are continuously transmitted are aligned to the next subframesof the SRS transmission candidate subframes indicated bysrs-SubframeConfig, as illustrated in FIG. 11, as in the firstembodiment, there is a possibility that the transmission efficiencydecreases depending on srs-SubframeConfig.

Accordingly, in the present embodiment, a description will be given of amethod for mapping the repetition signals in accordance withsrs-SubframeConfig and the parameter X and the retuning time (i.e., theparameter Y) without a reduction in the transmission efficiency.

Since a base station and a terminal according to the present embodimenthave the same basic configurations as those of the base station 100 andthe terminal 200 according to the first embodiment, a description willbe given using FIGS. 8 and 9.

The following description will be given of a case in which the SRStransmission period (T_(SFC)) is 5 or 10 and only one SRS transmissioncandidate subframe exists in the SRS transmission period (T_(SFC))(i.e., a case in which Δ_(SFC) has only one value), as in the firstembodiment. That is, a description will be given of a case ofsrs-SubframeConfig=3, 4, 5, 6, 9, 10, 11, 12 illustrated in FIG. 2.

The base station 100 indicates srs-SubframeConfig to the terminal 200 incell-specific higher layer signaling for setting an SRS resourcecandidate group.

The base station 100 also indicates the number of repetitions (N_(Rep))to the terminal 200 before PUSCH transmission/reception. The number ofrepetitions (N_(Rep)) may be indicated from the base station 100 to theterminal 200 via an UE-specific higher layer or may be indicated usingPDCCH for MTC.

The base station 100 also indicates the values of the parameter X andthe parameter Y to the terminal 200 before PUSCH transmission/reception.

The terminal 200 indicates repetition transmission on a PUSCH a numberof times corresponding to the number of repetitions (N_(Rep)) reportedfrom the base station 100. When the number of repetitions (N_(Rep)) islarger than X, the terminal 200 transmits the repetition signals in Xconsecutive subframes by using the same resource, then changes the 1.4MHz frequency band (an MTC narrowband) through frequency hopping, andagain transmits the repetition signals in X consecutive subframes byusing the same resource, as illustrated in FIG. 5. As illustrated inFIG. 5, a retuning time (e.g., corresponding to one subframe) isreserved during the frequency hopping.

In the present embodiment, the terminal 200 maps the repetition signals(i.e., the MTC narrowbands), transmitted in X consecutive subframes inPUSCH repetition transmission, to subframes so as not to overlap the SRStransmission candidate subframes indicated by srs-SubframeConfig.

In the present embodiment, for T_(SFC)≥nY (n is larger than or equal to2), the first subframe of a subset of n sets of X subframes in which therepetition signals are continuously transmitted is aligned to the nextsubframe of the corresponding SRS transmission candidate subframeindicated by srs-SubframeConfig. Also, the frequency hopping is allowedto be performed n-1 times in the SRS transmission period (T_(SFC)).

That is, the terminal 200 transmits, in units of X subframes, therepetition signals to be transmitted inn sets of X subframes in the SRStransmission period (T_(SFC)). In this case, each time n is reached, theterminal 200 aligns the first subframes of X subframes in which therepetition signals are continuously transmitted to the next subframes ofthe SRS transmission candidate subframes indicated bysrs-SubframeConfig. That is, the first subframe of a subset constitutedby n sets of X subframes is set in the next subframe of thecorresponding SRS transmission candidate subframe.

FIG. 12 illustrates a mapping example of signals in MTC narrowbands inthe case of srs-SubframeConfig=9, X=4, and Retuning time=1 subframe(i.e., Y=5). That is, in FIG. 12, a relationship T_(SFC)2×Y (n=2) issatisfied.

As illustrated in FIG. 12, the repetition signals are mapped to thesecond to fifth subframes, the seventh to 10th subframes, and the 12thto 15th subframes. In this case, as illustrated in FIG. 12, the firstsubframe of the second to fifth subframes and the first subframe of the12th to 15th subframes are the next subframes of SRS transmissioncandidate subframes. That is, as illustrated in FIG. 12, each time n=2is reached, the terminal 200 aligns the first subframe of X subframes inwhich the repetition signals are continuously transmitted to the nextsubframe of the SRS transmission candidate subframe indicated bysrs-SubframeConfig. The terminal 200 then performs frequency hopping n-1times in the SRS transmission period (T_(SFC)=10).

That is, the first subframe of a subset constituted by n=2 sets of Xsubframes is aligned to the next subframe of an SRS transmissioncandidate subframe. As a result, this subset is mapped to consecutivesubframes (in FIG. 12, nine subframes) that are not set in SRStransmission candidate subframes. Also, in this subset, frequencyhopping is performed once (i.e., n-1=1) in the SRS transmission period(T_(SFC))=10 subframes.

As described above, in the present embodiment, when the SRS transmissionperiod T_(SFC) is larger than or equal to n times of the value Yobtained by adding the value of X and the retuning time (n is an integergreater than or equal to 2), the first subframe of a subset constitutedby n sets of X subframes is set in the next subframe of an SRStransmission candidate subframe.

With this setting, in the SRS transmission period, the repetitionsignals can be mapped to subframes that are not set in an SRStransmission candidate subframe. Thus, it is possible to prevent areduction in the transmission efficiency as much as possible.

Also, as in the first embodiment, it is possible to avoid a collisionbetween a repetition transmission of an MTC coverage enhancementterminal and an SRS transmission of an existing system. As a result,since phase discontinuity does not occur in repetition transmissionsignals, cross-subframe channel estimation and symbol level combiningusing X subframes are performed in the base station 100 to thereby makeit possible to improve the channel estimation accuracy and the receptionquality.

In the present embodiment, a case in which the value of nY is smallerthan or equal to T_(SFC) (T_(SFC)≥nY) is assumed. That is, forsrs-SubframeConfig=3, 4, 5, 6 (a case in which T_(SFC) is 5 and thenumber of Δ_(SFC) is one), cross-subframe channel estimation and symbollevel combining over X=2 subframes work (however, only for X=Y), and forsrs-SubframeConfig=9, 10, 11, 12 (a case in which T_(SFC) is 10 and thenumber of Δ_(SFC) is one), cross-subframe channel estimation and symbollevel combining over X=2, 3, 4 subframes work.

Third Embodiment

Since a base station and a terminal according to the present embodimenthave the same basic configurations as those of the base station 100 andthe terminal 200 according to the first embodiment, a description willbe given using FIGS. 8 and 9.

The following description will be given of a case in which the SRStransmission period (T_(SFC)) is 2, 5, or 10 and only one SRStransmission candidate subframe exists in the SRS transmission period(T_(SFC)) (i.e., a case in which Δ_(SFC) has only one value). That is, adescription will be given of a case of srs-SubframeConfig=1, 2, 3, 4, 5,6, 9, 10, 11, 12 illustrated in FIG. 2.

Also, in the present embodiment, assume a case in which the value of Xis larger than the number of consecutive subframes that are not set inSRS transmission candidate subframes (a case in which the value of X islarger than or equal to the transmission period T_(SFC)). That is, forsrs-SubframeConfig=1, 2 (T_(SFC)=2), X≥2 is given; forsrs-SubframeConfig=3, 4, 5, 6 (T_(SFC)=5), X≥5 is given; and forsrs-SubframeConfig=9, 10, 11, 12 (T_(SFC)=10), X≥10 is given.

The base station 100 indicate srs-SubframeConfig to the terminal 200 incell-specific higher layer signaling for setting an SRS resourcecandidate group.

The base station 100 also indicates the number of repetitions (N_(Rep))to the terminal 200 before PUSCH transmission/reception. The number ofrepetitions (N_(Rep)) may be indicated from the base station 100 to theterminal 200 via an UE-specific higher layer or may be indicated usingPDCCH for MTC.

The base station 100 may also indicate the value of the parameter X tothe terminal 200 before PUSCH transmission/reception.

The terminal 200 performs repetition transmission on a PUSCH a number oftimes corresponding to the number of repetitions (N_(Rep)) reported fromthe base station 100. When the number of repetitions (N_(Rep)) is largerthan X, the terminal 200 transmits the repetition signals in Xconsecutive subframes by using the same resource, then changes the 1.4MHz frequency band (an MTC narrowband) through frequency hopping, andagain transmits the repetition signals in X consecutive subframes byusing the same resource, as illustrated in FIG. 5. As illustrated inFIG. 5, a retuning time (e.g., corresponding to one subframe) isreserved during the frequency hopping.

In this case, in PUSCH repetition transmission, the terminal 200 alignsthe first subframes of X subframes in which the repetition signals arecontinuously transmitted to the next subframes of the SRS transmissioncandidate subframes indicated by srs-SubframeConfig. Also, the terminal200 punctures a symbol that is a candidate to which an SRS is to bemapped, the symbol being included in the SRS transmission candidatesubframe of the subframes in which the repetition signals aretransmitted (in this case, the last SC-FDMA symbol in the subframe).

FIG. 13 illustrates a mapping example of signals in MTC narrowbands forsrs-SubframeConfig=3 and X=2. That is, in FIG. 13, T_(SFC)=X is given.

As illustrated in FIG. 13, each first subframe of X=2 subframes is setin the next subframe of an SRS transmission candidate subframe.

However, in FIG. 13, the value of X (X=2) is the same as the SRStransmission period T_(SFC) and is larger than the number of consecutivesubframes (one subframe) that are not set in an SRS transmissioncandidate subframe. Thus, one or more subframes (in FIG. 13, onesubframe) in the transmission segment in X subframes are SRStransmission candidate subframes. That is, when the value of X is largerthan or equal to the transmission period T_(SFC), there is a possibilitythat the repetition signals (data signals) and an SRS collide with eachother in one or more subframes.

As described above, the terminal 200 prevents a collision between an SRSand data signals, by not performing data transmission in the lastSC-FDMA symbol (an SRS resource candidate) in each SRS transmissioncandidate subframe. To this end, in the present embodiment, aftermapping data to 12 SC-FDMA symbols except for DMRSs in one subframeillustrated in FIG. 1, as in other subframes, the terminal 200 puncturesthe last SC-FDMA symbol as a format for transmitting data in SRStransmission candidate subframes.

The first subframe of X subframes in which the repetition signals arecontinuously transmitted is allocated to the next subframe of each SRStransmission candidate subframe indicated by srs-SubframeConfig, asdescribed above, and thus, in the case of X=T_(SFC), the last subframe(the second subframe) of the X subframes overlaps the SRS transmissioncandidate subframe, as illustrated in FIG. 13. Thus, the symbol in whichthe terminal 200 does not perform data transmission (i.e., the symbolthat is punctured) is only the last SC-FDMA symbol the last subframe ofX subframes.

As a result, phase discontinuity due to the puncture occurs only in onelast symbol in X subframes. In other words, phase continuity ismaintained in the symbols other than the last symbol in X subframes.Hence, it is possible to minimize an influence that the phasediscontinuity has on the cross-subframe channel estimation and thesymbol level combining over X subframes.

In contrast, in FIG. 13, if the first subframe of X=2 subframes in whichthe repetition signals are continuously transmitted is shifted forwardby one subframe, the first subframe of the X=2 subframes overlaps theSRS transmission candidate subframe, and thus the last SC-FDMA symbol inthe subframe is punctured. In this case, since the transmission-signalphase discontinuity occurs between the first subframe and the secondsubframe, the base station 100 cannot perform the cross-subframe channelestimation and the symbol level combining over the X=2 subframes.

As described above, the first subframe of X=2 subframes in which therepetition signals are continuously transmitted is aligned to the nextsubframe of an SRS transmission candidate subframe, as illustrated inFIG. 13, to thereby allow the base station 100 to perform thecross-subframe channel estimation and the symbol level combining overX=2 subframes (except for the last symbol in the second subframe),thereby making it possible to improve the channel estimation accuracyand the reception quality.

FIG. 14 illustrates a mapping example of signals in MTC narrowbands forsrs-SubframeConfig=3 and X=4. That is, in FIG. 14, T_(SFC)<X is given.

For X>T_(SFC), in the middle subframe of X subframes, data signalsoverlap SRS transmission candidate subframes. In FIG. 14, in twosubframes, that is, the second and fourth subframes, of X=4 subframes,data signals overlap SRS transmission candidate subframes. Accordingly,in FIG. 14, the terminal 200 punctures the last SC-FDMA symbols in thetwo subframes, that is, the second and fourth subframes, of the X=4subframes.

In this case, when a case in which the first subframe of the X=4subframes in which the repetition signals are continuously transmitted,as illustrated in FIG. 14, is shifted forward by one subframe isassumed, the last SC-FDMA symbols in the first and third subframes ofthe X=4 subframes are punctured. In this case, the transmission-signalphase discontinuity occurs between the first subframe and the secondsubframe, and further, the transmission-signal phase discontinuity alsooccurs between the third subframe and the fourth subframe. As a result,the cross-subframe channel estimation and the symbol level combiningover X=2 subframes can be performed only using the second and thirdsubframes.

In contrast, in the present embodiment, the first subframe of the X=4subframes is aligned to the next subframe of each SRS transmissioncandidate subframe indicated by srs-SubframeConfig, as illustrated inFIG. 14. As a result, the last SC-FDMA symbols in the second and fourthsubframes of X=4 subframes are punctured. In this case, although thenumber of SC-FDMA symbols punctured in the above-described assumption isthe same, the phase discontinuity occurs only between the secondsubframe and the third subframe.

Hence, the base station 100 can perform the cross-subframe channelestimation and the symbol level combining over X=2 subframes by using aset of the first and second subframes and a set of the third and fourthsubframes, thus making it possible to improve the channel estimationaccuracy and the reception quality.

As described above, in the present embodiment, the first subframe of Xsubframes in which the repetition signals are continuously transmittedis set in the next subframe of each SRS transmission candidate subframereported by srs-SubframeConfig. With this setting, it is possible tominimize an influence that the phase discontinuity has on thecross-subframe channel estimation and the symbol level combining over Xsubframes. Also, it is possible to improve the channel estimationaccuracy and the reception quality.

Fourth Embodiment

Since a base station and a terminal according to the present embodimenthave the same basic configurations as those of the base station 100 andthe terminal 200 according to the first embodiment, a description willbe given using FIGS. 8 and 9.

The following description will be given of a case in which the SRStransmission period (T_(SFC)) is 5 or 10 and two or more SRStransmission candidate subframes exist in the SRS transmission period(T_(SFC)) (i.e., a case in which Δ_(SFC) has two or more values). Thatis, a description will be given of a case of srs-SubframeConfig=7, 8,13, 14 illustrated in FIG. 2.

The base station 100 indicates srs-SubframeConfig to the terminal 200 incell-specific higher layer signaling for setting an SRS resourcecandidate group.

The base station 100 also indicates the number of repetitions (N_(Rep))to the terminal 200 before PUSCH transmission/reception. The number ofrepetitions (N_(Rep)) may be indicated from the base station 100 to theterminal 200 via an UE-specific higher layer or may be indicated usingPDCCH for MTC.

The base station 100 may also indicate the value of the parameter X tothe terminal 200 before PUSCH transmission/reception.

The terminal 200 performs repetition transmission on a PUSCH a number oftimes corresponding to the number of repetitions (N_(Rep)) indicatedfrom the base station 100. When the number of repetitions (N_(Rep)) islarger than X, the terminal 200 transmits the repetition signals in Xconsecutive subframes by using the same resource, then changes the 1.4MHz frequency band (an MTC narrowband) through frequency hopping, andagain transmits the repetition signals in X consecutive subframes byusing the same resource, as illustrated in FIG. 5. As illustrated inFIG. 5, a retuning time (e.g., corresponding to one subframe) isreserved during the frequency hopping.

In this case, in the PUSCH repetition transmission, the terminal 200aligns the first subframe of X subframes in which the repetition signalsare continuously transmitted to a subframe that is next to an SRStransmission candidate subframe indicated by srs-SubframeConfig and thatis not set in an SRS transmission candidate subframe.

FIG. 15 illustrates a mapping example of signals in MTC narrowbands forsrs-SubframeConfig=7 and X=2.

As illustrated in FIG. 15, for srs-SubframeConfig=7, the SRStransmission period (T_(SFC))=5 is given, and the number of SRStransmission candidate subframes in the SRS transmission period(T_(SFC)) is two (Δ_(SFC)={0, 1}). That is, the first subframe, thesecond subframe, the sixth subframe, the seventh subframe, . . . , the(5n+1)th subframe, and the (5n+2)th subframe are SRS transmissioncandidate subframes.

In this case, as illustrated in FIG. 15, the respective first subframesof X=2 subframes are set in the subframes that are next to the SRStransmission candidate subframes and that are other than the SRStransmission candidate subframes. In FIG. 15, the respective firstsubframes of X=2 subframes are the third subframe, the eighth subframe,. . . , and the (5n+3)th subframe.

Also, in FIG. 15, the value of X (X=2) is smaller than or equal to thenumber of consecutive subframes (three subframes) that are not set inthe SRS transmission candidate subframes. The same also applies to acase of srs-SubframeConfig=8 in which the transmission period (T_(SFC))and the number of Δ_(SFC) are the same as those in the case ofsrs-SubframeConfig=7. That is, in the case of srs-SubframeConfig=7, 8,it is possible to perform the cross-subframe channel estimation and thesymbol level combining over X=2 subframes.

That is, any of values that are smaller than or equal to the number ofconsecutive subframes that are not set in the SRS transmission candidatesubframes is set for the parameter X, which is a unit of processing forthe cross-subframe channel estimation and the symbol level combining.Thus, when the value of X is smaller than or equal to the number ofconsecutive subframes that are not set in the SRS transmission candidatesubframes, the terminal 200 can map the repetition signals to subframesother than the SRS transmission candidate subframes. Thus, the terminal200 can map the repetition signals transmitted in X consecutivesubframes in which the cross-subframe channel estimation and the symbollevel combining are to be performed, while avoiding the SRS transmissioncandidate subframes.

Also, in the example illustrated in FIG. 15, the first subframe of X=2subframes in which the repetition signals are continuously transmittedis set in the subframe that is next to an SRS transmission candidatesubframe and that is not set in an SRS transmission candidate subframe.With this setting, the terminal 200 can map the repetition signals bymaking best use of the consecutive subframes that are not set in SRStransmission candidate subframes. In particular, when the value of X issmaller than or equal to the number of consecutive subframes that arenot set in SRS transmission candidate subframes, the terminal 200 canmap the repetition signals, while reliably avoiding SRS transmissioncandidate subframes by setting the first subframe of X subframes in thesubframe that is next to the SRS transmission candidate subframe andthat is not set in the SRS transmission candidate subframe.

According to the present embodiment, even when there are a plurality ofSRS transmission candidate subframes in the SRS transmission period(T_(SFC)), it is possible to avoid a collision between a repetitiontransmission of an MTC coverage enhancement terminal and an SRStransmission of an existing system, as described above. As a result,since phase discontinuity does not occur in repetition transmissionsignals, cross-subframe channel estimation and symbol level combiningusing X subframes are performed in the base station 100 to thereby makeit possible to improve the channel estimation accuracy and the receptionquality.

In a case (not illustrated) in which the value of X is the same as orlarger than the number of consecutive subframes that are not set in SRStransmission candidate subframes, it is sufficient that after mappingdata to 12 SC-FDMA symbols except for DMRSs in one subframe illustratedin FIG. 1, as in other subframes, the terminal 200 punctures the lastSC-FDMA symbol (corresponding to an SRS resource candidate) as a formatfor transmitting data in SRS transmission candidate subframe, as in thethird embodiment. In this case, the first subframe of X subframes inwhich the repetition signals are continuously transmitted is aligned toa subframe that is next to an SRS transmission candidate subframeindicated by srs-SubframeConfig and that is not set in an SRStransmission candidate subframe, thereby making it possible to avoid aninfluence that the phase discontinuity has on the cross-subframe channelestimation and the symbol level combining or making it possible tominimize the influence, as in the third embodiment.

The above description has been given of each embodiment of the presentdisclosure.

In the above embodiment, the repetition transmission of PUSCH has beendescribed as one example, the repetition transmission is not limited toPUSCH and may be any signals that are transmitted in resources (MTCnarrowbands) for MTC terminals, as illustrated in FIGS. 11 to 15. Forexample, for repetition transmission of an uplink control channel(Physical Uplink Control Channel (PUCCH)), the repetition signals mayalso be transmitted, as in the first to fourth embodiments.Specifically, in PUCCH repetition, the first subframe of X subframes inwhich the repetition signals are continuously transmitted may be alignedto a subframe that is next to an SRS transmission candidate subframeindicated by srs-SubframeConfig or to a subframe that is next to an SRStransmission candidate subframe indicated by srs-SubframeConfig and thatis not set in an SRS transmission candidate subframe. With this setting,it is possible to prevent a collision between a PUCCH repetitiontransmission of an MTC coverage enhancement terminal and an SRS of anexisting system. Thus, the base station 100 can improve the channelestimation accuracy and the reception quality by performingcross-subframe channel estimation and symbol level combining. Also, asin the third and fourth embodiments, when one or more subframes collidewith an SRS transmission candidate subframe in a transmission segment inX subframes, the transmission may be performed using a Shortened PUCCHformat in order to avoid a collision with an SRS.

Also, in the above embodiment, the description has been given of a casein which the first subframe of X subframes in which the repetitionsignals are continuously transmitted is aligned to a subframe that isnext to the SRS transmission candidate subframe indicated bysrs-SubframeConfig or to a subframe that is next to the SRS transmissioncandidate subframe indicated by srs-SubframeConfig and that is not setin the SRS transmission candidate subframe. However, it is conceivablethat, in the standards, only the first subframe in which repetitionsignals are transmitted NRe_(p) times is defined. For example,definition may be performed such that the PUSCH repetition transmissionis to be started from an n+k subframe, where n is the last subframe in adownlink control channel (PDCCH) for MTC in which repetitiontransmission is performed (k indicates the next subframe of the SRStransmission candidate subframe reported by srs-SubframeConfig or asubframe that is next to the SRS transmission candidate subframereported by srs-SubframeConfig, that is not set in the SRS transmissioncandidate subframe, and that satisfies k≥4).

Also, the number of repetitions, the value of the parameter X or Y, andthe values of the parameters defined by srs-SubframeConfig, which areused in the above-described embodiments, are examples and are notlimited thereto.

Also, although the description in the embodiments has been given of anexample in which one aspect of the present disclosure is realized usinghardware, the present disclosure can also be realized using software incooperation with hardware.

Also, the individual functional blocks used in the description of theabove embodiments are typically realized as a large-scale integration(LSI), which is an integrated circuit. The integrated circuit maycontrol the individual functional blocks used in the description of theembodiments and may have an input and an output. The functional blocksmay be individually integrated into single chips or they may beintegrated into a single chip so as to include one or more thereof.Although the functional blocks are implemented as an LSI in this case,they may also be called an integrated circuit (IC), a system LSI, asuper LSI, or an ultra LSI depending on a difference in the degree ofintegration.

The scheme for implementing an integrated circuit is not limited to theLSI and may be realized with a dedicated circuit or a general-purposeprocessor. A field programmable gate array (FPGA) that can be programmedafter manufacture of an LSI or a reconfigurable processor that allowsreconfiguration of connections and settings of circuit cells inside anLSI may also be used.

In addition, when a technology for circuit integration that replaces LSIbecomes available with the advancement of semiconductor technology orother derivative technology, the functional blocks may naturally beintegrated using the technology. Application of biotechnology and so onare possible.

A terminal in the present disclosure has a configuration including: arepeater that generates repetition signals by repeating uplink signalsover a plurality of subframes; a controller that sets a timing fortransmitting the repetition signals, based on information indicating atransmission candidate subframe for an SRS used for measuring an uplinkreception quality; and a transmitter that transmits the repetitionsignals at the set timing.

In the terminal in the present disclosure, a base station performscoherent combining on the repetition signals every predetermined numberof subframes of the plurality of subframes; and a first subframe of thepredetermined number of subframes is a next subframe of the transmissioncandidate subframe.

In the terminal in the present disclosure, a base station performscoherent combining on the repetition signals every predetermined numberof subframes of the plurality of subframes; the predetermined number issmaller than a transmission period of the SRS; and the predeterminednumber of subframes are consecutive subframes that are not set in thetransmission candidate subframe.

In the terminal in the present disclosure, a base station performscoherent combining on the repetition signals every predetermined numberof subframes of the plurality of subframes; frequency hopping isperformed on the repetition signals every predetermined number ofsubframes; and a transmission period of the SRS is larger than or equalto n times of a value obtained by adding the predetermined number andthe number of subframes required for frequency-band switching in thefrequency hopping (n is an integer greater than or equal to 2), a firstsubframe of a subset constituted by an n sets of the predeterminednumber of subframes is a next subframe of the transmission candidatesubframe.

In the terminal in the present disclosure, in the transmission period ofthe SRS, frequency hopping is performed on the repetition signals (n-1)times.

In the terminal in the present disclosure, a base station performscoherent combining on the repetition signals every predetermined numberof subframes of the plurality of subframes; and when the predeterminednumber is larger than or equal to the transmission period of the SRS,the controller punctures a symbol that is a candidate to which the SRSis to be mapped, the symbol being included in the transmission candidatesubframe of subframes in which the repetition signals are transmitted.

In the terminal in the present disclosure, a base station performscoherent combining on the repetition signals every predetermined numberof subframes of the plurality of subframes; and a first subframe of thepredetermined number of subframes is a subframe that is next to thetransmission candidate subframe and that is other than the transmissioncandidate subframe.

A base station in the present disclosure has a configuration including:a controller that sets a timing at which a terminal transmits repetitionsignals generated by repeating uplink signals over a plurality ofsubframes, based on information indicating a transmission candidatesubframe for an SRS used for measuring an uplink reception quality; areceiver that receives the repetition signals; and a combiner thatperforms in-phase combining on the repetition signals in the pluralityof subframes, based on the set timing.

A transmission method in the present disclosure includes: generatingrepetition signals by repeating uplink signals over a plurality ofsubframes; setting a timing for transmitting the repetition signals,based on information indicating a transmission candidate subframe for anSRS used for measuring an uplink reception quality; and transmitting therepetition signals at the set timing.

A reception method in the present disclosure includes: setting a timingat which a terminal transmits repetition signals generated by repeatinguplink signals over a plurality of subframes, based on informationindicating a transmission candidate subframe for an SRS used formeasuring an uplink reception quality; receiving the repetition signals;and performing coherent combining on the repetition signals in theplurality of subframes, based on the set timing.

One aspect of the present disclosure is useful for mobile communicationssystems and so on.

1. A terminal apparatus comprising: control circuitry, which, inoperation, generates physical uplink shared channel (PUSCH) repetitionsignals by repeating a PUSCH; and a transmitter, which is coupled to thecontrol circuitry and which, in operation, transmits the PUSCHrepetition signals in a plurality of subframes using a frequencyhopping; wherein the frequency hopping is performed on the PUSCHrepetition signals every X number of consecutive subframes, wherein X issignaled by a base station.
 2. The terminal apparatus according to claim1, wherein the control circuitry, in operation, punctures a last SC-FDMA(single-carrier frequency-division multiple access) symbol in a soundingreference signal (SRS) transmission candidate subframe out of theplurality of subframes, wherein the SRS transmission candidate subframeis signaled by the base station.
 3. The terminal apparatus according toclaim 2, wherein an SRS is transmitted in the last SC-FDMA symbol of theSRS transmission candidate subframe.
 4. The terminal apparatus accordingto claim 2, wherein the SRS transmission candidate subframe is inaccordance with an SRS transmission period (T_(SFC)) signaled by thebase station.
 5. The terminal apparatus according to claim 1, whereinthe control circuitry, in operation, generates physical uplink controlchannel (PUCCH) repetition signals by repeating a PUCCH; and thetransmission circuitry, in operation, transmits the PUCCH repetitionsignals in a plurality of subframes using a shortened PUCCH format. 6.The terminal apparatus according to claim 1, wherein X subframes areequal to or less than Y subframes, wherein Y is a frequency hoppingperiod signaled by the base station.
 7. The terminal apparatus accordingto claim 6, wherein Y frequency hopping period consists of X consecutivesubframes of the PUSCH repetition signals and zero or more retuning timesubframes.
 8. The terminal apparatus according to claim 6, wherein Xequals Y.
 9. A communication method comprising: generating physicaluplink shared channel (PUSCH) repetition signals by repeating a PUSCH;and transmitting the PUSCH repetition signals in a plurality ofsubframes using a frequency hopping; wherein the frequency hopping isperformed on the PUSCH repetition signals every X number of consecutivesubframes, wherein X is signaled by a base station.
 10. Thecommunication method according to claim 9, comprising: puncturing a lastSC-FDMA (single-carrier frequency-division multiple access) symbol in asounding reference signal (SRS) transmission candidate subframe out ofthe plurality of subframes, wherein the SRS transmission candidatesubframe is signaled by the base station.
 11. The communication methodaccording to claim 10, wherein an SRS is transmitted in the last SC-FDMAsymbol of the SRS transmission candidate subframe.
 12. The communicationmethod according to claim 10, wherein the SRS transmission candidatesubframe is in accordance with an SRS transmission period (T_(SFC))signaled by the base station.
 13. The communication method according toclaim 9, comprising: generating physical uplink control channel (PUCCH)repetition signals by repeating a PUCCH; and transmitting the PUCCHrepetition signals in a plurality of subframes using a shortened PUCCHformat.
 14. The communication method according to claim 9, wherein Xsubframes are equal to or less than Y subframes, wherein Y is afrequency hopping period signaled by the base station.
 15. Thecommunication method according to claim 14, wherein Y frequency hoppingperiod consists of X consecutive subframes of the PUSCH repetitionsignals and zero or more retuning time subframes.
 16. The communicationmethod according to claim 14, wherein X equals Y.